1. Field of the Invention
The present invention relates to a gamma conversion circuit which converts input-output characteristics especially in accordance with needs of users.
2. Description of the Prior Art
A gamma conversion circuit converts an input-output voltage in order to realize characteristics, especially those which users need. Such a gamma conversion circuit generally undergoes linear approximation with a differential amplifier circuit comprising an emitter resistance, but in recent years circuit design which can freely change gain setting of gamma conversion has been required.
Conventionally, in supposing the case that a gamma conversion curb is approximated with three straight lines, each block is configured by a differential amplifier circuit with emitter resistances RElb and RE2b as shown in FIG. 12.
Incidentally, a block diagram covering from an input (Vin) to an output (Vout) will be one as shown in FIG. 13 in which the above described differential amplifier circuit (FIG. 12) with an emitter resistance undergoes three-stage cascade connection.
However, the conventional has problems described below.
Each block, which is a differential amplifier circuit with an emitter resistance as shown in FIG. 12, can only undergo offsets adjustment in up-to-down and left-to-right directions as shown in FIG. 14 even if an external setting differential voltage V2 is changed. FIG. 14 shows three kinds of offset settings, and when an external setting voltage V2 for each block is adjusted, an input-output characteristics will be indicated in black dots and a thick line in FIG. 14.
A first problem of this circuit configuration (FIG. 12 and FIG. 13) is that the linear portion which approximates a gamma conversion curb is configured by a differential amplifier circuit with an emitter resistance. This will make it difficult to attain a gamma conversion curb having a free gain since any combination of various external setting voltages V2 will only stay within an adjustment range as in FIG. 15.
A reason therefor is that a differential amplifier circuit with an emitter resistance can not alter inclination of a line with the external setting voltage V2.
A second problem is that due to a circuit configuration in which a gain is set with a resistance the gain changes in accordance with dispersion of resistance in a product, thus a yield factor will decrease.
By contemplating such problems, the present invention is achieved and objects thereof are to provide a gamma conversion circuit characterized by a gamma conversion curb having a free gain and with a high yield factor of products.
A gamma conversion circuit of the present invention comprises: an input terminal; an output terminal; and a plurality of variable gain circuits each coupled between the input terminal and the output terminal, each having an operation amplifier circuit inputting two input voltages and producing an output voltage;
wherein gain of said output voltage changes in accordance with a difference between two input voltages.
A gamma conversion circuit of the present invention comprises: an input terminal; an output terminal; and a plurality of a voltage controlled amplifiers each coupled between the input terminal and the output terminal, each inputting an input voltage, a gain setting voltage, and a region setting voltage, and outputting an output voltage;
wherein the gain setting voltage sets an increasing rate of a gain of the output voltage during a unit period, the region setting voltage sets an amplifying operation region of the output voltage.
A gamma conversion circuit having a voltage controlled amplifier, the amplifier comprises: a first differential amplifier responding a gain setting voltage to produce a first control signal; a second differential amplifier responding an input voltage and a region setting voltage to produce a second control signal; and a third differential amplifier responding the first control signal and the second control signal to produce an output signal.